# Aktuelle Veranstaltungen

## Kolloquium

Thema:

### Shine a light! When matter shatters

Datum:

08.06.20

Uhrzeit:

16:15

Ort:

cyberspace

Vortragender:

Prof. Dr. Tetyana Galatyuk

Inhalt:

The microscopic properties of strong-interaction matter under extreme conditions of temperature and density is a topic of great interest. Matter in equilibrium radiates photons with a thermal spectrum revealing its temperature in the slope of the energy distribution. This is generalized for virtual photons, which materialize after a short time by creation of a pair of charged leptons (dileptons), for which their invariant mass takes the role of the energy as observable. In contrast to the case of photons, their spectral distribution is not affected by a blue (or red) shift. Moreover, dileptons offer the unique opportunity also to directly monitor in-medium electromagnetic spectral functions. Hence, dilepton spectra from strong-interaction medium reflect not only its temperature but also are sensitive to possible effects of a restoration of the spontaneously broken chiral symmetry. This talk will discuss important experimental results obtained so far at various facilities and the latest theoretical developments on emissivity of matter.

Ansprechpartner:

F. Karsch/TR211

## Kolloquium Mathematische Physik

Thema:

### The problem of latency in estimating the Covid-19 replication number

Datum:

08.05.20

Uhrzeit:

16:15

Ort:

ZOOM/Konferenzschaltung

Vortragender:

University of Texas at Austin

Inhalt:

Figuring out how to restart the world's economy without a resurgence of disease depends on understanding how contagious Covid-19 really is. However, estimates of the basic replication number $R_0$ vary greatly, with well-respected groups publishing estimates whose 95% confidence intervals don't even overlap. In this talk I'll go over the basic SIR and SEIR models of disease spread and present several different ways to treat the latency period between being exposed and becoming infectious. Simple SEIR models are unstable; working with a fixed set of data, small changes to the model can result in large changes to the estimated value of $R_0$. More realistic models are more complicated and are even less stable. The upshot is that we know much less about $R_0$ than is generally believed, and the error bars on the high side are particularly large. Containing the outbreak for an extended period may be a lot harder than our leaders think.

Ansprechpartner:

Gähler, Dr. Franz

## Seminar Hochenergiephysik

Thema:

### Observation of excess electron-recoil events in XENON1T

Datum:

16.07.20

Uhrzeit:

14:15

Ort:

cyberspace

Vortragender:

Christian Wittweg

Muenster

Inhalt:

XENON1T was a xenon dual-phase time projection chamber for WIMP Dark Matter searches and set world-leading limits for numerous Dark Matter candidates and interactions. It finished taking data at Laboratori Nazionali del Gran Sasso in 2018 and will be superseded by XENONnT later this year. In this seminar we present the latest results from a search for solar axions, axion-like particles (ALPs) and the magnetic moment of solar neutrinos. XENON1T was primarily designed to look for nuclear recoils from interactions of WIMPs with xenon atoms, but with its unprecedented low electron recoil background of $76 \pm 2$ events/(tonne $\times$ year $\times$ keV) in the energy range of 1–30 keV, it can probe new parameter space for such interactions of solar axions, neutrinos, and ALPs. The search in our recent paper, arXiv:2006.09721, revealed an excess of events below 7 keV, which is where the corresponding signals from electron recoils would be expected. The tested signal hypotheses are favored over background with significances of $3.5\sigma$ for solar axions, $3.0\sigma$ global ($4.0\sigma$ local) for ALP dark matter with a peak at $2.3 \pm 0.2$ keV (68 $\%$ C.L.), and $3.2\sigma$ for a neutrino magnetic moment. If one of these findings were to be confirmed, it would mean a long awaited piece of new physics. Our recent paper also discusses other explanations including the previously unconsidered $\beta$-decay of tritium. In this talk we review the detection principles, cross-checks of our results, and discuss the physics implications as well as alternative background hypotheses.

Ansprechpartner:

Ch. Schmidt

## Seminar Kondensierte Materie

Thema:

### 22-05-2020-14.15 hrs - D5-153 - Construction of tight binding models from ab initio calculations using maximally localized Wannier functions

Datum:

22.05.20

Uhrzeit:

14:15

Ort:

D5-153

Vortragender:

Thomas Benkenstein

Universtität Bielefeld

Inhalt:

Ansprechpartner:

Thomas Dahm

## Seminar Mathematische Physik

Thema:

### Statistics of Extremes in Eigenvalue-counting Staircases

Datum:

04.06.20

Uhrzeit:

16:00

Ort:

ZOOM / Konferenzschaltung

Vortragender:

Yan Fyodorov

King's College London

Inhalt:

We consider the counting function (“spectral staircase”) for eigenvalues of a random unitary matrix, drawn from the corresponding beta-ensemble. Our goal is to characterize the statistics of maximum deviation of this staircase from its mean slope in a fixed interval, when size of the matrix N >>1. We will show that one-sided extremes can be addressed by exploiting a mapping onto the statistical mechanics of log-correlated random processes and using an extended Fisher-Hartwig conjecture. The resulting statistics exhibits combined features of counting statistics of Fermions with Sutherland-type interaction and extremal statistics of the fractional Brownian motion with Hurst index H = 0. Some of the features are expected to be universal. The talk is based on the paper Fyodorov-Le Doussal arXiv:2001.04135.

Ansprechpartner:

Gernot Akemann

## Seminar Bielefeld-Melbourne Zufallsmatrizen

Thema:

### The level spacing in the chGUE - from the hard edge to the bulk

Datum:

15.07.20

Uhrzeit:

09:00

Ort:

ZOOM / Konferenzschaltung

Vortragender:

Valentin Gorski

Universität Bielefeld

Inhalt:

We consider the level spacing in the chGUE with added characteristic polynomials and give an integral representation for the spacing between the k-th and (k-1)-st eigenvalue at finite N and in the large N limit, together with numerical checks for larger k. We further study the transition from the hard edge to the bulk, i. e. when Wigners surmise is applicable and the dependence on the number of characteristic polynomials for this transition.

Ansprechpartner:

Gernot Akemann

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